Answers for Week 1 Discussion
1. 1) Acute, chronic
2) Acute
3) Acute, Chronic
4) Chronic
5) Evolutionary
6) Evolutionary
7) Evolutionary
8) Evolutionary
2. Vestigial structures represent a case of historical inheritance. They may have
been adaptive in the past, but are now neutral or detrimental traits.
3. There is a size related phenotypic correlation with metabolism and many other
traits.
4. The size-corrected residual represents the amount by which an animal deviates
from the expected value of a trait, given its body size. Using Fig. 1.8, the Plains
zebra has a high positive size-corrected residual, meaning that it has an unusually
high gestation period for an animal of its body size. The Bushbuck, on the other
hand, has a residual near 0, indicating that the gestation period of this species is
similar to what is predicted from a regression of other ungulates.
5. Not likely. Probably historical inheritance. Could test by comparing Wood
ducklings with other, ground nesting ducklings, or even other precoccial birds.
6. The first explanation is lacking mechanism, the second is lacking origin.
7. These animals started with different parts, which explains why they have different
wing structures.
8. Regulation: Adv. The internal environment is kept constant, which allows the
body’s components to function under constant conditions. Disadv. Energetically
costly. Conformity: Adv. Energetically cheap. Disadv. The internal environment
is not constant, thus the components of the body must function under a variety of
conditions.
9. Animals are structurally dynamic
10. Genotype 2 would respond best to a hot climate, Genotype 1 would respond best
to a cooler climate. In an area with hot summers and cold winters, Genotype 3
would be the most frequent because the ability of this genotype to acclimate to
different temperatures would allow individuals to better survive and reproduce
than their less flexible counterparts.
11. We would observe a genetic cline as we went from low to high latitudes. At the
equator, Genotype 2 would be the most common. It would become progressively
less common at higher latitudes, and at temperate latitudes, genotype 3 would
begin to dominate. As we reached the arctic, genotype 1 would take over as the
dominant genotype. If genotype 2 were the only genotype, we would not see such
a cline. Changes in genetic frequency depend on existing genetic variation. The
population may not even be able to colonize higher latitudes because of its lack of
evolvability and modest plasticity.
12. Tropical waters are warm, and oxygen is less soluble in warm water. In addition,
many microbes that use oxygen thrive in warmer water with high amounts of
detritus. Finally, in many tropical areas, primary productivity is high above
ground, which can shade the body of water and inhibit phytoplankton growth,
thus cutting off a potential source of oxygen in the water. Warm waters also have
less mixing than waters at higher latitudes, because the temperature remains
constant. Mixing allows for nutrients to cycle more effectively and thus promotes
phytoplankton growth. Lastly, tropical fish always have access to the air-water
interface. Other fish may have barriers at certain times of the year, such as when
ice forms.
13. A Leopard Frog would need to seek a favorable microenvironment within the
meadow. It might stay in areas of tall grass, a microenvironment with reduced
wind speed, lower solar radiation, and higher humidity. This microenvironment
would slow the speed of desiccation.
14. The allele that codes for sickle cell anemia also provides resistance to malaria, a
common disease in Sub-Saharan Africa. The disease only manifests itself in
those individuals homozygous for the allele, but disease resistance is conferred to
heterozygotes. This example of pleitropy, confers a greater fitness benefit to
carriers of the allele.
15. We can infer that the presence of wings across 3 different unrelated taxa suggests
that wings are adaptive for an aerial lifestyle. This method of searching for
similar physiological features across taxa to infer adaptation is the comparative
method.
16. In natural selection in the laboratory, only the environment is manipulated by the
experimenter, and individuals are able to breed freely, whereas during artificial
selection, the experimenter manipulates the breeding success of certain
individuals by selectively choosing individuals that will or will not breed.
17. Marine invertebrates are osmoconformers, thus the composition of their body
fluids is similar to the ambient water. As long as the sea does not freeze, they will
not freeze. Fish are osmoregulators, thus their freezing point is higher than the
sea around them. Without special protections, they could freeze even if the sea
around them remained liquid.
18. Negative Feedback